1. Field of the Invention
The invention relates to a method for determining an energy yield loss of a first wind turbine of a wind farm comprising a plurality of wind turbines.
2. Description of Related Art
Particularly in the case of large wind farms it is desirable to offer a customer an energy yield guarantee instead of an availability guarantee. Here, in the case of a failure of a wind turbine, or respectively merely a reduced power output of a wind turbine, that is, a wind turbine that is operated in a reduced energy yield mode, it is however difficult to quantify the lost energy yield. Here, the lost energy yield is the difference between the actual possible energy yield in the case of an energy-optimized normal operating mode and the actual energy yield of a wind turbine, which is operated in a reduced energy yield mode or even fails, or respectively is operated without energy yield. It is, however, difficult to determine the actual energy yield that would be possible in an energy-optimized normal operating mode. For this purpose an exact wind strength profile based on location and time at the wind turbine, which is operated in a reduced energy yield mode, would have to be created which is impossible to do exactly, and can be approximated with known methods, such as for example, a nacelle anemometer or a plurality of nacelle anemometers in the region of the wind turbine, only in a very inaccurate way.
With an existing wind measurement mast in the proximity of the wind turbine or the wind farm, using an existing wind turbine power curve, the energy yield can be calculated with the assumption that the wind in the rotor plane corresponds to the wind at the measurement mast. This method is however based on the assumption that does not correspond to reality, and in particular in the case of wind farms, is also too imprecise. In addition, the approach to use the nacelle anemometer of the wind turbine operated in reduced energy yield mode is too imprecise, because the anemometer measurement is strongly distorted by the nacelle and possibly also the rotor blades of wind turbines, which are present in close proximity.